MAI MOTOMONTANT DE LA MAMWITHIN US009823053B1

( 12 ) United States Patent ( 10 ) Patent No . : US 9 , 823 , 053 B1 ( 45 ) Date of Patent : Nov . 21 , 2017 Fink

( 54 ) SOLID - FUEL RAMJET AMMUNITION 4 , 539 , 911 A 4 , 745 , 740 A 4 , 796 , 534 A *

9 / 1985 Flatau 5 / 1988 Dunn et al . 1 / 1989 Mikhail . . . . . . . . . . . . . . . ( 71 ) Applicant : The Boeing Company , Chicago , IL

( US )

F42B 10 / 26 102 / 374

5 , 067 , 406 A 5 , 423 , 179 A 5 , 544 , 586 A

11 / 1991 Olson et al . 6 / 1995 Gunners et al . 8 / 1996 Huerta ( 72 ) Inventor : Lawrence E . Fink , Renton , WA ( US )

FOREIGN PATENT DOCUMENTS ( 73 ) Assignee : The Boeing Company , Chicago , IL ( US )

DE 8 / 1985 . . . . . . . . . . . . . . F42B 15 / 00 EP - 0151676 A2 * * cited by examiner ( * ) Notice : Subject to any disclaimer , the term of this patent is extended or adjusted under 35

U . S . C . 154 ( b ) by 0 days .

( 21 ) Appl . No . : 15 / 250 , 538 Primary Examiner — Stephen Johnson Assistant Examiner — Joshua T Semick ( 74 ) Attorney , Agent , or Firm — Ostrager Chong Flaherty & Broitman P . C .

( 22 ) Filed : Aug . 29 , 2016 ( 51 )

( 52 )

Int . CI . F42B 15 , 00 ( 2006 . 01 ) F42B 5 / 10 ( 2006 . 01 ) FO2K 7 / 10 ( 2006 . 01 ) U . S . CI . CPC . . . . . . . . . . . . . . . . F42B 15 / 00 ( 2013 . 01 ) ; F42B 5 / 10

( 2013 . 01 ) ; F02K 7 / 10 ( 2013 . 01 ) Field of Classification Search CPC . . . . . . . . . . . . . . . F42B 15 / 00 ; F42B 5 / 10 ; FO2K 7 / 10 See application file for complete search history .

( 58 )

( 57 ) ABSTRACT A ramjet projectile comprising : an outer assembly that is tubular and comprises first , second and third portions ; solid ramjet fuel attached to and disposed inside the first portion of the outer assembly ; an inner assembly disposed inside the outer assembly and comprising a first portion threadably coupled to the second portion of the outer assembly and a second portion surrounded by the third portion of the outer assembly to form an annular air passageway having an air inlet . The first portion of the inner assembly comprising a plurality of openings spatially distributed about a circum ference . The inner assembly is rotatable relative to the outer assembly between first and second locations displaced by a distance from each other during travel along the gun barrel . The openings are not in flow communication with the annular air passageway when the inner assembly is at the first location and are in flow communication with the annular air passageway when the inner assembly is at the second location . Preferably the solid ramjet fuel comprises boron and a binder .

( 56 ) References Cited U . S . PATENT DOCUMENTS

2 , 935 , 946 A * 5 / 1960 Gallo 2 , 989 , 919 A * 6 / 1961 Engborg . . . . . . . . . . . . . . .

FO2K 7 / 10 102 / 374

FO2K 9 / 92 102 / 379

3 , 024 , 729 A 3 , 726 , 219 A 4 , 428 , 293 A

3 / 1962 Kluge 4 / 1973 Bolick 1 / 1984 Botwin et al . 20 Claims , 5 Drawing Sheets

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SOLID - FUEL RAMJET AMMUNITION mately four times the specific impulse ( the product of thrust and time divided by propellant weight ) as compared to solid

BACKGROUND rocket propellant . The higher specific impulse translates to either longer range for a given payload weight and volume ,

The technology disclosed herein generally relates to 5 greater payload to a given range , a smaller size to a given ammunition . More particularly , the technology disclosed range , or a combination of all three compared to a solid herein relates to gun - launched ramjet projectiles . rocket motor . Gun range is a key element of weapon and mission One aspect of the subject matter disclosed in detail below

effectiveness . Increased range gives the potential to leverage is a ramjet projectile comprising : an outer assembly that is an overmatch advantage where the soldier or pilot can 10 tubular and comprises first , second and third portions ; solid engage the enemy at a range that is greater than the range of ramjet fuel attached to and disposed inside the first portion enemy fire . The greater the range , the more time the soldier of the outer assembly ; an inner assembly disposed inside the or pilot has and the more shots can be made before coming outer assembly and comprising a first portion threadably in range of an approaching enemy . Increased maximum coupled to the second portion of the outer assembly and a range also usually translates into benefits of a flatter trajec - 15 second portion surrounded by the third portion of the outer tory and increased striking velocity at a given range for assembly to form an annular air passageway having an air potentially increased effectiveness . Ammunition range may inlet , the first portion of the inner assembly comprising a be increased by raising muzzle velocity with longer tubes , plurality of openings spatially distributed about a circum using higher - energy propellants or higher working pres - ference , wherein the inner assembly is rotatable relative to sures , using boosted projectiles , or by improving the ballistic 20 the outer assembly between a first location and a second coefficient by reducing drag . location displaced by a distance from the first location , the

There is a need to extend the lethal capabilities of openings being not in flow communication with the annular medium - caliber cannon munitions within a multitude of air passageway when the inner assembly is at the first deployment scenarios . location and being in flow communication with the annular

25 air passageway when the inner assembly is at the second SUMMARY location . Preferably solid ramjet fuel comprises boron and a

binder . The subject matter disclosed in detail below is directed to In accordance with one embodiment of the ramjet pro

the development of onboard propulsion that will signifi - jectile described in the preceding paragraph , the inner cantly extend the range of cannon ammunition ( e . g . , 30 assembly comprises a threaded - tube air valve and an inlet medium - caliber ammunition having a caliber of 20 - 60 mm ) , centerbody threadably coupled to the threaded - tube air using solid ramjet fuel . However , the concept and technol - valve , wherein the first portion of the inner assembly is part ogy disclosed below is not limited to use in medium - caliber of the threaded - tube air valve and the second portion of the cannon ammunition and is applicable to a wide range of inner assembly is part of the inlet centerbody . In addition , ammunition size . 35 the outer assembly comprises : an outer body having a

Ramjets require a rocket booster , or gun launch , to forward end comprising a circular cylindrical outer surface achieve a flight condition where thrust is greater than drag , and a concave annular inner surface ; and an inlet cowl joined which for missiles is approximately Mach 2 , at which point to the circular cylindrical outer surface of the forward end of the ramjet is capable of accelerating to higher speed . Since the outer body , wherein the first and second portions of the the ramjet propulsion system depends only on its forward 40 outer assembly are parts of the outer body , and the third motion at supersonic speed to compress intake air , the portion of the outer assembly is formed by the inlet cowl and engine flow - path components have no moving parts . Con - the forward end of the outer body . The threaded - tube air sequently , it has inherent simplicity , reliability , light weight , valve comprises a first set of threads for threadably coupling and high - speed flight capability not possible with other to the outer assembly and a second set of threads for air - breathing engines . These attributes make the ramjet a 45 threadably coupling to the inlet centerbody , wherein a hand good choice for propelling medium - caliber cannon ammu - edness of the first set of threads is specified such that rotation nition at supersonic speed . of the outer body will cause forward translation of the

In a solid - fuel ramjet , air from the inlet flows through the threaded - tube air valve and inlet centerbody , whose own “ pipe ” of fuel ( also known as a “ fuel grain ” ) , which burns rotation will lag that of the outer body due to its inertia . The along its length . In accordance with a preferred embodiment 50 handedness of the first set of threads is opposite the hand disclosed in detail below , a solid - fuel ramjet projectile is edness of the second set of threads to avoid unscrewing of provided comprising an outer assembly which is rotatable the inlet centerbody when the threaded - tube air valve relative to the inner assembly , causing the inner assembly to reaches a thread runout . displace in a forward direction relative to the outer assembly Another aspect of the subject matter disclosed in detail during gun launch . The inner assembly comprises a center - 55 below is an ammunition cartridge comprising : a cartridge body and a threaded - tube air valve that provides a structur - case comprising a cylindrical wall ; an outer assembly that is ally robust centerbody support without needing side support tubular and comprises first , second and third portions , the struts . Boron solid ramjet fuel , disposed inside the outer first portion of the outer assembly being disposed inside and assembly and rearward of the threaded - tube air valve , is in contact with the cylindrical wall of the cartridge case , used to propel the ramjet projectile through the atmosphere . 60 wherein the first portion of the outer assembly comprises a Prior to firing , the gun propellant is disposed inside the circular cylindrical inner surface ; solid ramjet fuel attached ramjet combustion chamber to provide volume efficiency . to and disposed inside the first portion of the outer assembly ,

The approach disclosed herein uses on - board , air - breath wherein the solid ramjet fuel is an annular layer on the ing propulsion to extend range . Unlike solid rocket propel - circular cylindrical inner surface ; an inner assembly dis lant whose formulation is approximately 20 % fuel and 80 % 65 posed inside the outer assembly and comprising a first oxidizer , the solid ramjet fuel disclosed herein is 100 % fuel portion threadably coupled to the second portion of the outer and obtains oxidizer from air , with the result being approxi assembly and a second portion surrounded by the third

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portion of the outer assembly to form an annular air pas - FIG . 3 is a diagram representing an external isometric sageway having an air inlet , the first portion of the inner view of a three - dimensional ( 3 - D ) model of the ammunition assembly comprising a plurality of openings spatially dis - cartridge depicted in FIG . 1 . tributed about a circumference and inner surfaces that bound F IG . 4 is a cutaway diagram representing a 3 - D model of a space inside the first portion of the inner assembly that is 5 an ammunition cartridge in its in - gun configuration . Ele in flow communication with the openings , wherein the inner ments of the inner and outer assemblies have been removed assembly is rotatable relative to the outer assembly between to reveal the propellant . a first location and a second location displaced by a distance FIG . 5 is a cutaway diagram representing a 3 - D model of from the first location , the openings being not in flow a ramjet projectile in its in - flight configuration . Elements of communication with the annular air passageway when the 10 an outer assembly have been removed to reveal the com inner assembly is at the first location and being in flow bustion chamber and the inner assembly in an extended communication with the annular air passageway when the position . inner assembly is at the second location ; and propellant FIG . 6 is a cutaway diagram representing a 3 - D model of occupying at least an interior space bounded in part by a the outer body of the ramjet projectile depicted in FIG . 2 . A portion of the cartridge case and the solid ramjet fuel . In 15 portion of the outer body has been removed to reveal its accordance with one embodiment , the propellant further internal structure . occupies at least a portion of the space inside the first portion FIG . 7 is a cutaway diagram representing a 3 - D model of of the inner assembly . Preferably , the solid ramjet fuel the threaded - tube air valve of the ramjet projectile depicted comprises boron and a binder . in FIG . 2 . A portion of the threaded - tube air valve has been

A further aspect of the subject matter disclosed in detail 20 removed to reveal its internal structure . below is a method of propelling a ramjet projectile , com Reference will hereinafter be made to the drawings in prising : ( a ) placing an ammunition cartridge in a rifled bore which similar elements in different drawings bear the same of a gun barrel , the ammunition cartridge containing pro - reference numerals . pellant and solid ramjet fuel and comprising a cartridge case and a ramjet projectile comprising an outer assembly that is 25 DETAILED DESCRIPTION partly encased by the cartridge case and an inner assembly disposed inside the outer assembly to form an annular Illustrative embodiments of gun - launched ramjet ammu channel ; ( b ) igniting the propellant inside the ammunition nition are described in some detail below . However , not all cartridge while openings in the inner assembly of the ramjet features of an actual implementation are described in this projectile are not in flow communication with the annular 30 specification . A person skilled in the art will appreciate that channel ; ( c ) combusting the propellant to propel the ramjet in the development of any such actual embodiment , numer projectile along the rifled bore of the gun barrel ; ( d ) causing ous implementation - specific decisions must be made to the outer assembly of the ramjet projectile to rotate relative achieve the developer ' s specific goals , such as compliance to the inner assembly while the ramjet projectile is being with system - related and business - related constraints , which propelled along the rifled bore of the gun barrel ; ( e ) causing 35 will vary from one implementation to another . Moreover , it the inner assembly to displace in a forward direction relative will be appreciated that such a development effort might be to the outer assembly as the outer assembly rotates relative complex and time - consuming , but would nevertheless be a to the inner assembly so that the openings are in flow routine undertaking for those of ordinary skill in the art communication with an annular channel between the inner having the benefit of this disclosure . and outer assemblies after the ramjet projectile has exited a 40 FIG . 1 is a diagram representing a partially sectioned view muzzle of the gun barrel ; and ( f ) combusting the solid ramjet of an ammunition cartridge 10 in accordance with one fuel inside the outer assembly of the ramjet projectile to embodiment . FIG . 3 is a diagram representing an external propel the ramjet projectile forward through an atmosphere . isometric view of a 3 - D model of the ammunition cartridge In accordance with one embodiment , step ( e ) comprises 10 depicted in FIG . 1 . using threads on an inner surface of the outer assembly to 45 Referring to FIG . 1 , the ammunition cartridge 10 is shown deflect threads on an outer surface of the inner assembly in in its in - gun configuration . In this embodiment , the ammu the forward direction as the outer assembly rotates relative nition cartridge 10 comprises a cartridge case 2 and a ramjet to the inner assembly . projectile 12 ( shown in isolation in FIG . 2 ) . The cartridge

Other aspects of ramjet ammunition and methods for case 2 comprises a cylindrical wall 4 and a case head 6 that propelling ramjet projectiles are disclosed below . 50 closes one end of the cylindrical wall 4 , the other end being

open . The cartridge 10 further comprises an electric primer BRIEF DESCRIPTION OF THE DRAWINGS 44 , which is inserted into a recess in the center of the base

6 of the cartridge case 2 . Upon application of sufficient The features , functions and advantages discussed in the voltage , the primer 44 ignites the propellant 14 ( see FIG . 4 ) ,

preceding section can be achieved independently in various 55 thereby firing the ramjet projectile 12 . The ramjet projectile embodiments or may be combined in yet other embodi - 12 comprises a tubular outer assembly and an inner assem ments . Various embodiments will be hereinafter described bly that rotates and displaces in a forward direction relative with reference to drawings for the purpose of illustrating the to the outer assembly when fired . above - described and other aspects . The outer assembly of the ramjet projectile 12 comprises

FIG . 1 is a diagram representing a partially sectioned view 60 a tubular outer body 20 having a nozzle 38 at its rearward of an ammunition cartridge comprising a ramjet projectile in end . The outer body 20 is the main structure of the ramjet accordance with one embodiment . The ammunition car - projectile 12 . A major portion of outer body 20 is submerged tridge is shown in its in - gun configuration . in ( i . e . , surrounded by ) the cylindrical wall 4 of the cartridge

FIG . 2 is a diagram representing a partially sectioned view case 2 to provide the length and volume needed for ramjet of the ramjet projectile of the ammunition cartridge depicted 65 fuel and combustion . The cylindrical wall 4 of the cartridge in FIG . 1 . The ramjet projectile is shown in its in - flight case 2 is attached to outer body 20 by conventional means . configuration . More specifically , two cannelure ( i . e . , crimping grooves ) are

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provided in the outer body 20 into which the cylindrical wall of the helical grooves with the rotation band 36 in the gun 4 is crimped during final assembly . The crimp attachment barrel causes the outer body 20 ( and the inlet cowl 22 fixedly ensures that the projectile remains in place and attached to coupled thereto ) to rotate inside the gun barrel as the ramjet the cartridge case 2 during rough handling , and it enables the projectile 12 travels along its length . The inertia of the inner initial pressure caused by the burning propellant to rise to a 5 assembly as the outer assembly rotates causes the threaded sufficient level for reliable and consistent firing before tube air valve 16 to not rotate in tandem with the outer body giving way . An annular ring of solid ramjet fuel 32 is 20 ( to which the threaded - tube air valve 16 is threadably disposed adjacent to a circular cylindrical internal surface of coupled ) . Due to the threaded coupling , any rotation of the the outer body 20 . The outer assembly further comprises an outer body 20 relative to the threaded - tube air valve 16 ( and inlet cowl 22 ( not surrounded by the cylindrical wall 4 ) that 10 the inlet centerbody 18 threadably coupled thereto ) causes is attached to the forward end of outer body 20 . The forward the inner assembly to displace in a forward direction relative end of the inlet cowl 22 has a conical internal surface . to the outer assembly , i . e . , from the relative position shown

The inner assembly of the ramjet projectile 12 comprises in FIG . 1 to the relative position shown in FIG . 2 . a threaded - tube air valve 16 that is threadably coupled to FIG . 2 is a diagram representing a partially sectioned view threads disposed on the internal surface of a threaded portion 15 of the ramjet projectile 12 in its in - flight configuration , i . e . , of the outer body 20 . The threaded - tube air valve 16 after the ramjet projectile 12 has exited the gun muzzle . In comprises a circular cylindrical wall . A first portion of the this configuration , the inner assembly has moved in a cylindrical wall of the threaded - tube air valve 16 has exter - forward direction relative to the outer assembly to an extent nal threads for coupling with the outer body 20 ; a second that the openings 34 are no longer covered by the outer body portion of the cylindrical wall of the threaded - tube air valve 20 20 . In this position , the interior volumes that are respectively 16 has a plurality of circumferentially distributed openings surrounded by the solid ramjet fuel 32 and the threaded - tube 34 formed therein . In the position shown in FIG . 1 , these air valve 16 form a combustion chamber 30 , where com openings 34 are covered by the outer body 20 . This covering bustion of the solid ramjet fuel 32 occurs during flight . In the of the openings 34 prevents the escape of gun gas from position shown in FIG . 2 , the threaded - tube air valve 16 chamber 8 into the air passageway 24 while the ramjet 25 admits air from the annular air passageway 24 into the projectile 12 is traveling along the length of the gun barrel combustion chamber 30 via openings 34 , thereby providing ( not shown in FIG . 1 ) . In FIG . 1 ( and other drawings ) , the the oxidizing agent required for combustion of the solid openings 34 are depicted as being rectangular to simplify the ramjet fuel 32 . The inside diameter of the solid ramjet fuel drawings . However , in a preferred embodiment , each of 32 matches the throat diameter of the nozzle 38 to facilitate openings 34 would have rounded forward and aft ends to 30 casting the fuel without the complexity of an expanding avoid stress concentration at the corners of the opening . mandrel .

Still referring to FIG . 1 , the inner assembly further In the position shown in FIG . 2 , the tip of the inlet comprises an inlet centerbody 18 having a threaded portion centerbody 18 projects forward of the lip of the inlet cowl 40 that is threadably coupled to threads disposed on the 22 , which has the effect of increasing inlet efficiency by external surface of a forwardmost portion of the threaded - 35 providing oblique , external shock waves rather than a single tube air valve 16 . The inlet centerbody 18 is disposed inside normal shock . This kind of design is well - known to those the inlet cowl 22 . The forward end of the inlet centerbody 18 skilled in inlet design . Another feature of the translating inlet has a conical external surface . The inlet centerbody 18 and centerbody 18 is that the overall length of the assembly inlet cowl 22 are configured to form an annular air passage - loaded in the gun is constrained . By extending the inlet way 24 having a double - cone , all - external compression air 40 centerbody 18 after firing , a few extra millimeters of effec inlet 26 . In accordance with the embodiment depicted in tive length is acquired , which results in more fuel length FIG . 1 , the inlet centerbody 18 has a chamber 28 that available as compared to a non - translating design . contains an explosive charge . In alternative embodiments FIG . 4 is a cutaway diagram representing a 3 - D model of ( e . g . , for purely kinetic weapons ) , the chamber 28 may be the ammunition cartridge 10 in its in - gun configuration . eliminated . The inlet centerbody 18 may comprise a main 45 Elements of the inner and outer assemblies have been body that is open at the forward end and a nose cap 42 that removed to reveal the gun propellant 14 . The gun propellant is attached to and closes the open end of the main body . The 14 may comprise a double - base ball propellant powder threaded - tube air valve 16 , inlet centerbody 18 , outer body mixture containing nitrocellulose and nitroglycerin as explo 20 and inlet cowl 22 are preferably made of a hard metal sive components . The gun propellant powder occupies the alloy ( e . g . , 4340 alloy steel with Rockwell C hardness 40 ) . 50 volume inside the cartridge case 2 and initially fills the

Prior to launch of the ramjet projectile 12 , the cylindrical ramjet combustion chamber 30 ( see FIG . 2 ) . wall 4 and case head 6 of cartridge case 2 , the solid ramjet FIG . 5 is a cutaway diagram representing a 3 - D model of fuel 32 , and the threaded - tube air valve 16 define a chamber a ramjet projectile 12 in its in - flight configuration . Portions 8 that is filled with gun propellant in powder form ( not of the outer assembly have been removed to reveal the shown in FIG . 1 , but see gun propellant 14 in FIG . 5 ) . The 55 combustion chamber 30 , the solid ramjet fuel 32 and the ammunition cartridge 10 further comprises a rotation band inner assembly in an extended position . The inlet centerbody 36 that is seated in and affixed to an annular groove formed 18 is hollowed - out from the front and has a thin - wall nose in the external surface of the outer body 20 . cap 42 . The inlet centerbody 18 and inlet cowl 22 are

Preferably the rotation band 36 is made of a metal or configured to form an air passageway 24 having a double metal alloy ( e . g . , copper or aluminum ) that will be deformed 60 cone , all - external compression air inlet 26 . The inlet cowl 22 by helical grooves formed in the internal surface of the gun is press - fit onto the outer body 20 . A steel shim is optionally barrel when the propellant inside chamber 8 is ignited and used between the forward end of the threaded - tube air valve the ramjet projectile 12 is propelled along the length of the 16 and the inlet centerbody 18 to adjust the critical longi gun barrel while the cartridge case 2 remains behind . It is tudinal distance between the tip of the extended inlet cen planned for the residual hot gun gas and hot air total 65 terbody 18 and the tip of inlet cowl 22 . temperature to ignite the solid ramjet fuel 32 . As the ramjet In accordance with the embodiment depicted in FIG . 5 , projectile 12 travels toward the gun muzzle , the interaction the openings 34 in the threaded - tube air valve 16 comprise

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eight longitudinal slots circumferentially distributed at equal translation of the threaded - tube air valve 16 and inlet angular intervals . During flight of the ramjet projectile 12 , centerbody 18 , whose own rotation will lag that of the outer atmospheric air enters the air inlet 26 and flows in sequence body 20 due to its inertia . The handedness of the threads of through the annular air passageway 24 , the openings 34 , and the externally threaded circular cylindrical portion 16a is the combustion chamber 30 . This air flow provides oxidizing 5 opposite the handedness of the threads of the externally agent for the combustion of the solid ramjet fuel 32 inside threaded circular cylindrical portion 16b to avoid unscrew the combustion chamber 30 . The combustion products are ing of the inlet centerbody 18 when the threaded - tube air then ejected out the nozzle 38 , propelling the ramjet pro valve 16 reaches the thread runout 16c . In accordance with jectile forward . one implementation , the ammunition cartridge 10 depicted

Preferably the solid ramjet fuel 32 is castable high - energy 10 in FIG . 1 can be designed to fit the application of the 30 - mm BMF - 013 fuel , which is commercially available from Aero - M789 ammunition in the M230 weapon system ( Apache jet Rocketdyne , Sacramento , Calif . The formulation of helicopter gun ) without modification to the gun . The double BMF - 013 fuel is 50 % boron in a hydroxyl - terminated polyb - cone , all - external compression air inlet 26 is designed to utadiene binder . This fuel formulation has a density of 0 . 05 operate at Mach 1 . 85 . A design issue for the threaded - tube 1b / cu inch and a heating value of 20 , 040 Btu / lb . The ability 15 air valve 16 is to avoid stripping of threads due to the high of the solid ramjet fuel to withstand the high - acceleration in - barrel pressure . Standard 18x1 . 0 mm left - handed threads environment may be improved by changing to an epoxy were used with an effective engagement length of 9 . 5 mm , binder . Either a burn rate increase of 70 % to maintain a accounting for missing threads due to the openings 34 , and circular port , or a perimeter factor of 1 . 7 ( i . e . fuel “ spokes ” ) , exceed the minimum design requirement of 8 . 7 mm . or combination , is predicted to be required compared to the 20 The inner assembly ( i . e . , threaded - tube air valve 16 and baseline fuel burning rate . Higher burning rates have been inlet centerbody 18 ) relies on its inertia to cause it to lag the demonstrated with additives to BMF - 013 , and a grain design initial outer body rotation ( caused by engagement of the with perimeter factor up to about 2 . 0 is feasible . BMF - 013 rotation band 36 with the gun barrel rifling ) , to extend the fuel is known to auto - ignite at the 510° F . ( 266° C . ) initial inlet centerbody 18 forward because of the threads , and air total temperature , but a small amount of energetic 25 make an air flow path through the openings 34 and the inside material at the head end of the fuel grain , such as a sliver of of threaded - tube air valve 16 , into the ramjet combustion rocket propellant ignited by residual hot gun gas , or a poison chamber 30 . pill igniter ( a heat - triggered safety feature used to ignite The threaded - tube air valve 16 is initially submerged one rocket propellant before full onset of oxidizer decomposi - thread pitch length into the outer body 20 to maintain a seal tion ) can be used to mitigate risk and ensure . 30 for the time the ramjet projectile 12 is in the gun barrel ( less

The boron solid ramjet fuels represent the state of the art . than one revolution ) . The threaded - tube air valve 16 is fully Prior to their development , an all - hydrocarbon fuel desig - open ( as seen in FIG . 5 ) approximately 0 . 01 second after nated UTF - 18 , 818 was the standard . Though lower in heat - leaving the gun barrel . Since the ramjet projectile 12 spins ing value and density than boron fuel , it is still viable and it clockwise ( viewed from the rear ) , the threads between the ( or a similar all - hydrocarbon fuel like the Aerojet Rocket - 35 threaded - tube air valve 16 and outer body 20 are left dyne BMF - 003 ) is an alternative to the boron fuels . handed . The threaded - tube air valve 16 is solid forward of

FIG . 6 is a cutaway diagram representing a 3 - D model of the openings 34 . The externally threaded circular head 16b the outer body 20 of the ramjet projectile depicted in FIGS . seen in FIG . 7 has standard 13 - mm right - handed threads to 2 and 5 . A portion of the outer body 20 has been removed securely attach the inlet centerbody 18 when the thread to reveal its internal structure . The outer body 20 comprises 40 runout at the 18 - mm - threaded aft end of the threaded - tube a circular cylindrical portion 20a that surrounds the annular air valve 16 engages the outer body 20 and causes the inlet ring of solid ramjet fuel ( not shown in FIG . 6 ) , an internally centerbody 18 to rotate to match the rotation of the outer threaded ring - shaped portion 20b and a concave ring - shaped body 20 . The thickness of the threaded - tube air valve 16 portion 20c that forms the rearwardmost portion of the matches the required step - height for a downstream recircu annular air passageway 24 seen in FIGS . 2 and 5 . The nozzle 45 lation zone and adequate flameholding for fuel combustion . 38 is integrally formed with the circular cylindrical portion The technology disclosed hereinabove has strong transi

tion potential for multi - service application in a wide - range FIG . 7 is a cutaway diagram representing a 3 - D model of of guns for ground , ship , and air platforms . The only

the threaded - tube air valve 16 of the ramjet projectile discriminating requirement is a muzzle velocity on the order depicted in FIGS . 2 and 5 . A portion of the threaded - tube air 50 of at least 500 m / sec . valve 16 has been removed to reveal its internal structure . To summarize some of the aspects disclosed above , one The threaded - tube air valve 16 comprises an externally method of propelling a ramjet projectile is characterized by threaded circular cylindrical portion 16a having openings the following steps : ( a ) placing an ammunition cartridge in 34 , an externally threaded circular head 16b and a thread a rifled bore of a gun barrel , the ammunition cartridge runout 16c . The threads of the externally threaded circular 55 containing propellant and solid ramjet fuel and comprising cylindrical portion 16b have a diameter less than the diam - a cartridge case and a ramjet projectile comprising an outer eter of the threads of the externally threaded circular head assembly that is partly encased by the cartridge case and an 16a to provide clearance for assembly . In the assembled inner assembly disposed inside the outer assembly to form state , the threads of the externally threaded circular cylin - an annular channel ; ( b ) igniting the propellant inside the drical portion 16a interengage the opposing threads of the 60 ammunition cartridge while openings in the inner assembly internally threaded ring - shaped portion 20b , while the of the ramjet projectile are not in flow communication with threads of the externally threaded circular head 16b interen - the annular channel ; ( c ) combusting the propellant to propel gage the opposing threads of an internally threaded ring - the ramjet projectile along the rifled bore of the gun barrel ; shaped portion 40 ( visible in FIGS . 2 and 4 ) of the inlet ( d ) causing the outer assembly of the ramjet projectile to centerbody 18 . The handedness of the threads of the exter - 65 rotate relative to the inner assembly while the ramjet pro nally threaded circular cylindrical portion 16a is specified jectile is being propelled along the rifled bore of the gun such that rotation of the outer body 20 will cause forward barrel ; ( e ) causing the inner assembly to displace in a

20a .

US 9 , 823 , 053 B1 10

forward direction relative to the outer assembly as the outer wherein the inner assembly is rotatable relative to the assembly rotates relative to the inner assembly so that the outer assembly between a first location and a second openings are in flow communication with an annular chan location displaced by a distance from the first location , nel between the inner and outer assemblies after the time the openings being not in flow communication with the when the ramjet projectile has exited a muzzle of the gun 5 annular air passageway when the inner assembly is at barrel ; and ( f ) combusting the solid ramjet fuel inside the the first location and being in flow communication with outer assembly of the ramjet projectile as the ramjet pro the annular air passageway when the inner assembly is jectile exits the muzzle of the gun barrel to propel the ramjet at the second location . projectile forward through an atmosphere . In particular , step 2 . The ramjet projectile as recited in claim 1 , wherein an ( e ) comprises using threads on an inner surface of the outer 10 inner surface of the third portion of the outer assembly has assembly to deflect threads on an outer surface of the inner a circular profile of varying radius , and an outer surface of assembly in the forward direction as the outer assembly the second portion of the inner assembly has a circular rotates relative to the inner assembly . Steps ( c ) , ( d ) and ( e ) profile of varying radius . are performed concurrently .

For avoidance of doubt concerning support for the various 15 3 . The ramjet projectile as recited in claim 1 , wherein terms which appear in the appended apparatus claims , the inner surfaces of the first portion of the inner assembly following correlation of claim limitations with disclosed bound a space which is in flow communication with the structure is provided : ( 1 ) the circular cylindrical portion 20a annular air passageway via the openings when the inner of outer body 20 is the structure corresponding to the first assembly is at the second location . portion of the outer assembly recited in the claims ; ( 2 ) the 20 4 . The ramjet projectile as recited in claim 3 , wherein the internally threaded ring - shaped portion 20b of outer body 20 first portion of the outer assembly comprises a circular is the structure corresponding to the second portion of the cylindrical inner surface , and the solid ramjet fuel is an outer assembly recited in the claims ; ( 3 ) the a concave annular layer on the circular cylindrical inner surface that ring - shaped portion 20c of outer body 20 and the inlet cowl bounds a chamber which is adjacent to and in flow com 22 are the structures corresponding to the third portion of the 25 munication with the space inside the first portion of the inner outer assembly recited in the claims ; ( 4 ) the externally assembly . threaded circular cylindrical portion 16a of threaded - tube air 5 . The ramjet projectile as recited in claim 4 , wherein the valve 16 is the structure corresponding to the first portion of first portion of the outer assembly further comprises an the inner assembly recited in the claims ; and ( 5 ) the inlet outlet having a minimum radius less than a radius of the centerbody 18 is the structure corresponding to the second 30 in inner surface of the first portion of the outer assembly . portion of the inner assembly recited in the claims . 6 . The ramjet projectile as recited in claim 1 , wherein the While ramjet projectiles and methods of ramjet propul inner assembly comprises a tapered nose that does not sion have been described with reference to various embodi ments , it will be understood by those skilled in the art that project forward of the outer assembly when the inner various changes may be made and equivalents may be 35 as assembly is at the first location and that projects forward of substituted for elements thereof without departing from the the outer assembly when the inner assembly is at the second teachings herein . In addition , many modifications may be location . made to adapt the concepts and reductions to practice 7 . The ramjet projectile as recited in claim 1 , wherein the disclosed herein to a particular situation . Accordingly , it is solid ramjet fuel comprises boron and a binder . intended that the subject matter covered by the claims not be 40 8 . The ramjet projectile as recited in claim 1 , wherein the limited to the disclosed embodiments . inner assembly comprises a threaded - tube air valve and an

The process claims set forth hereinafter should not be inlet centerbody threadably coupled to the threaded - tube air construed to require that the steps recited therein be per - valve , wherein the first portion of the inner assembly is part formed in alphabetical order ( any alphabetical ordering in of the threaded - tube air valve and the second portion of the the claims is used solely for the purpose of referencing 45 inner assembly is part of the inlet centerbody . previously recited steps ) or in the order in which they are 9 . The ramjet projectile as recited in claim 8 , wherein the recited . Nor should they be construed to exclude portions of threaded - tube air valve comprises a first set of threads for two or more steps ( such as the steps of combusting propel - threadably coupling to the outer assembly and a second set lant , causing the outer assembly of the ramjet projectile to of threads for threadably coupling to the inlet centerbody , rotate relative to the inner assembly , and causing the inner 50 wherein a handedness of the first set of threads is opposite assembly to displace relative to the outer assembly ) being a handedness of the second set of threads . performed concurrently . 10 . The ramjet projectile as recited in claim 8 , further

comprising an explosive charge housed inside the inlet The invention claimed is : centerbody . 1 . A ramjet projectile comprising : 55 11 . The ramjet projectile as recited in claim 1 , wherein the an outer assembly that is tubular and comprises first , outer assembly comprises : second and third portions ; an outer body having a forward end comprising a circular

solid ramjet fuel attached to and disposed inside the first cylindrical outer surface and a concave annular inner portion of the outer assembly ; surface ; and

an inner assembly disposed inside the outer assembly and 60 an inlet cowl joined to the circular cylindrical outer comprising a first portion threadably coupled to the surface of the forward end of the outer body , second portion of the outer assembly and a second wherein the first and second portions of the outer assem portion surrounded by the third portion of the outer bly are parts of the outer body , and the third portion of assembly to form an annular air passageway having an the outer assembly is formed by the inlet cowl and the air inlet , the first portion of the inner assembly com - 65 forward end of the outer body . prising a plurality of openings spatially distributed 12 . The ramjet projectile as recited in claim 1 , wherein the about a circumference , second portion of the outer assembly closes the openings

15 Secor

US 9 , 823 , 053 B1 12

when the inner assembly is at the first location and does not an outer body having a forward end comprising a circular close the openings when the inner assembly is at the second cylindrical outer surface and a concave annular inner location . surface ; and

13 . An ammunition cartridge comprising : an inlet cowl joined to the circular cylindrical outer a cartridge case comprising a cylindrical wall ; 5 surface of the forward end of the outer body , an outer assembly that is tubular and comprises first , wherein the first and second portions of the outer assem

second and third portions , the first portion of the outer bly are parts of the outer body , and the third portion of assembly being disposed inside and in contact with the the outer assembly is formed by the inlet cowl and the cylindrical wall of the cartridge case , wherein the first forward end of the outer body . portion of the outer assembly comprises a circular 10 cylindrical inner surface ; 18 . The ammunition cartridge as recited in claim 13 ,

solid ramjet fuel attached to and disposed inside the first wherein the second portion of the outer assembly closes the portion of the outer assembly , wherein the solid ramjet openings when the inner assembly is at the first location and fuel is an annular layer on the circular cylindrical inner does not close the openings when the inner assembly is at the surface ; second location .

an inner assembly disposed inside the outer assembly and 19 . A method of propelling a ramjet projectile , compris comprising a first portion threadably coupled to the ing : second portion of the outer assembly and a second ( a ) placing an ammunition cartridge in a rifled bore of a portion surrounded by the third portion of the outer gun barrel , the ammunition cartridge containing pro assembly to form an annular air passageway having an 20 pellant and solid ramjet fuel and comprising a cartridge air inlet , the first portion of the inner assembly com case and a ramjet projectile comprising an outer assem prising a plurality of openings spatially distributed bly that is partly encased by the cartridge case and an about a circumference and inner surfaces that bound a inner assembly disposed inside the outer assembly to space inside the first portion of the inner assembly that form an annular channel ; is in flow communication with the openings , wherein 25 ( b ) igniting the propellant inside the ammunition cartridge the inner assembly is rotatable relative to the outer while openings in the inner assembly of the ramjet assembly between a first location and a second location projectile are not in flow communication with the displaced by a distance from the first location , the annular channel ; openings being not in flow communication with the ( c ) combusting the propellant to propel the ramjet pro

jectile along the rifled bore of the gun barrel ; annular air passageway when the inner assembly is at 30 the first location and being in flow communication with ( d ) causing the outer assembly of the ramjet projectile to the annular air passageway when the inner assembly is rotate relative to the inner assembly while the ramjet at the second location ; and projectile is being propelled along the rifled bore of the

propellant occupying at least an interior space bounded in gun barrel ; part by a portion of the cartridge case and the solid 35 ( e ) causing the inner assembly to displace in a forward ramjet fuel . direction relative to the outer assembly as the outer

14 . The ammunition cartridge as recited in claim 13 , assembly rotates relative to the inner assembly so that wherein the propellant further occupies at least a portion of the openings are in flow communication with an annu the space inside the first portion of the inner assembly . lar channel between the inner and outer assemblies

15 . The ammunition cartridge as recited in claim 13 , 40 after the ramjet projectile has exited a muzzle of the wherein the solid ramjet fuel comprises boron and a binder . gun barrel ; and

16 . The ammunition cartridge as recited in claim ( f ) combusting the solid ramjet fuel inside the outer 13 , wherein the inner assembly comprises a threaded - tube air assembly of the ramjet projectile to propel the ramjet valve and an inlet centerbody threadably coupled to the projectile forward through an atmosphere . threaded - tube air valve , wherein the first portion of the inner 45 20 . The method as recited in claim 19 , wherein step ( e ) assembly is part of the threaded - tube air valve and the comprises using threads on an inner surface of the outer second portion of the inner assembly is part of the inlet assembly to deflect threads on an outer surface of the inner centerbody . assembly in the forward direction as the outer assembly

17 . The ammunition cartridge as recited in claim 13 , rotates relative to the inner assembly . wherein the outer assembly comprises : * * * *